1. Technical Field
The inventive arrangements relate generally to video systems and more particularly to video systems that record or play back digitally encoded video sequences.
2. Description of Related Art
Many televisions employ the interlaced scanning technique. Under this format, the video signal is typically divided into a predetermined number of horizontal lines. During each field period, only one-half of these lines are scanned; generally, the odd-numbered lines are scanned during the first field period, and the even-numbered lines are scanned during the next field period. Each sweep is referred to as a field, and when combined, the two fields form a complete picture or frame. For an NTSC system, sixty fields are displayed per second, resulting in a rate of thirty frames per second.
As a moving object moves across the screen in an interlaced scanning television, each field will only display a portion of the moving object. This partial display occurs because a field only displays every other horizontal line of the overall picture. For example, for a particular field n, only the odd-numbered horizontal lines are scanned, and the portion of the moving object that will be displayed in field n is the portion that is scanned during the odd-numbered horizontal line sweep for field n. The next field, field n+1, is created 1/60 of a second later and will display the even-numbered horizontal lines of the picture. Thus, the portion of the moving object that is displayed in field n+1 is the portion that is scanned during the even-numbered horizontal line sweep for field n+1. Although each field is temporally distinct, the human eye perceives the sequential display of the fields as smooth motion due to the speed at which the fields are displayed.
If a viewer activates a trick mode while viewing interlaced video, the trick mode video signal may contain repeated non-progressive pictures. For example, if the viewer initiates a slow trick mode, each non-progressive picture can be repeated a predetermined number of times to create a slow motion effect. The display of each repeated non-progressive picture, however, is in accordance with the normal display of a non-progressive picture, i.e, the fields that make up the non-progressive picture are alternately displayed. As an example, if a non-progressive picture were to be repeated three times (and assuming that the top field is displayed first), the repeated display of the picture would follow this order: top field, bottom field; top field, bottom field; and top field, bottom field.
If a moving object appears in the pictures recorded under the interlaced scanning format, each field will display the moving object in one specific position. Thus, as these fields are alternately displayed during the slow motion trick mode, the moving object in the display rapidly moves from one position in the display to another; in effect, the moving object appears to vibrate. This phenomenon, commonly referred to as a vibration artifact, is created because the interlaced fields are temporally distinct, and the moving object appears in a different position for each field.
This problem is also present in certain televisions that include a deinterlacer. As is known in the art, a deinterlacer can construct complete frames from an interlaced field. Thus, a deinterlacer can construct complete frames out of the fields that comprise the repeated non-progressive frame. Nevertheless, these complete frames constructed from the interlaced fields will also be displayed in an alternate fashion thereby creating the possibility of the vibration artifact. In addition, this vibration effect appears in not only a slow trick mode but may also be present in any other trick mode in which non-progressive pictures are repeated, such as a freeze trick mode. Thus, it is desirable to eliminate the vibration artifact without increasing system costs or complexity.